Faculty Publications
Permanent URI for this communityhttps://idr.nitk.ac.in/handle/123456789/18736
Publications by NITK Faculty
Browse
11 results
Search Results
Item Continuous operation of fluidized bed bioreactor for biogenic sulfide oxidation using immobilized cells of Thiobacillus sp(Asian Network for Scientific Information, 2007) Ravichandra, P.; Mugeraya, G.; Anupoju, G.R.; Ramakrishna, M.; Jetty, A.In the present study, obligate autotrophic Thiobacillus sp. was isolated from aerobic sludge distillery effluent treatment plant and the experiments were conducted in a fluidized bed bioreactor for the biological oxidation of sulfide using Ca-alginate immobilized Thiobacillus sp. All the experiments were conducted in continuous mode at different sulfide loading rates 0.018, 0.02475, 0.03375, 0.03825 and 0.054 and different hydraulic retention times 5, 3.67, 2.67, 2.35 and 1.67 h by varying flow rates 2.4×10-4, 3.3×10-4, 4.5×10-4, 5.1 × 10-4 and 7.2×10-4. Sulfide conversions higher than 90% were obtained at almost all sulfide loading rates and hydraulic retention times. All the experiments were conducted at constant pH of around 6 and temperature of 30±5°C. © 2007 Asian Network for Scientific Information.Item Biological treatment of toxic petroleum spent caustic in fluidized bed bioreactor using immobilized cells of thiobacillus RAI01(2008) Potumarthi, R.; Mugeraya, G.; Jetty, A.In the present studies, newly isolated Thiobacillus sp was used for the treatment of synthetic spent sulfide caustic in a laboratory-scale fluidized bed bioreactor. The sulfide oxidation was tested using Ca-alginate immobilized Thiobacillus sp. Initially, response surface methodology was applied for the optimization of four parameters to check the sulfide oxidation efficiency in batch mode. Further, reactor was operated in continuous mode for 51 days at different sulfide loading rates and retention times to test the sulfide oxidation and sulfate and thiosulfate formation. Sulfide conversions in the range of 90-98% were obtained at almost all sulfide loading rates and hydraulic retention times. However, increased loading rates resulted in lower sulfide oxidation capacity. All the experiments were conducted at constant pH of around 6 and temperature of 30?±?5 °C. © 2008 Humana Press.Item Minimum superficial fluid velocity in a gas-solid swirled fluidized bed(2010) Harish Kumar, S.; Murthy, D.V.R.A swirl flow is achieved in a bed of solids by passing air through multiple fluid inlets, which are tangentially located at the base of a flat-based circular column. The minimum superficial velocities needed to achieve swirling of the bed are measured experimentally under varied conditions. An empirical correlation for the minimum swirl velocity has been proposed. The results indicate that a stable swirling regime operation of the bed is possible. There exists an upper limit of static bed depth beyond which stable swirling of entire bed is not possible. The minimum swirl velocities are found to be 1.2-1.3 times the minimum fluidization velocities predicted for conventional fluidized beds. © 2010 Elsevier B.V.Item Modified PGC model and its validation by experiments for heat and moisture transfer analysis in a vertical fluidized desiccant bed(Elsevier Ltd, 2015) Ramzy K, A.; Kadoli, R.Air dehumidification in fluidized beds utilizing desiccants is an alternative for the refrigeration methods. A variety of pseudo gas controlled (PGC) model are proposed by assuming constant and varying temperature as well as water content for the solid phase to evaluate the conditions of exit air during adsorption processes. Experimental tests for moisture adsorption in silica gel fluidized bed are carried out. The modified PGC model that assumes uniform water content, varying temperature and linear porosity distributions along the bed estimates the temporal average bed water content to agree very well with the experimental data. The RMSE of the numerical results of the present model ranges from 0.2 to 6% and that obtained from the isothermal model are in the range of 6%-68%. © 2015 Elsevier Ltd. All rights reserved.Item Color Indistinction Method for the Determination of Devolatilization Time of Large Fuel Particles in Chemical Looping Combustion(American Chemical Society service@acs.org, 2019) Pragadeesh, K.S.; Ruben Sudhakar, D.R.Chemical looping combustion (CLC) is one of the promising fuel conversion technologies for carbon capture with low energy penalty. Devolatilization is an important physical phenomenon occurring during solid fuel CLC. Devolatilization behavior influences fragmentation, combustion rate, emission, and particulates generation in fluidized bed CLC (FB-CLC), thus a critical input for its design. Existing visual techniques for determining devolatilization time cannot be applied in CLC conditions because of its flameless combustion nature. In the present study, a new, simple, and quick technique called "color indistinction method" (CIM) is proposed for the determination of devolatilization time (?d) in FB-CLC, where the end of devolatilization is inferred from the disappearance of fuel particle in a hot fluidized bed. Single-particle devolatilization studies in FB-CLC are conducted to determine the devolatilization time using CIM for two types of fuels, viz., coal and biomass (Casuarina equisetifolia wood), of size range 8-25 and 10-20 mm, respectively, at three different fuel reactor bed temperatures (800, 875, and 950 °C) and one fluidization velocity. The proposed technique is validated in three ways: (i) the measurement of residual volatiles present in char by thermogravimetric analysis; (ii) mass loss history of the fuel during devolatilization; and (iii) diagnostics using particle center temperature measurements. The results of CIM experiments, in terms of degree of error involved, are compared with an established flame extinction technique (FET) and a more accurate particle center temperature (PCT) method. The amount of volatiles released during devolatilization, as determined by CIM, is 91.3% for coal and 98.9% for biomass. These values compare very well with the results of the established FET, in which the volatile release is 90.7% for coal and 99.1% for biomass samples. The devolatilization times determined using CIM are in line with particle center temperature measurements with an acceptable error range of -7.57 to +3.70%. The proposed CIM is successful in establishing the devolatilization time of different fuels in CLC conditions and can also be applied in other flameless combustion conditions. © 2019 American Chemical Society.Item Computational investigation of hydrodynamics and solid circulation in fluidized bed column(Taylor and Francis Ltd., 2021) Sriniketh, A.; Ali, A.A.Gas–solid fluidized beds are commonly used in applications where high heat and mass transfer is required, which are influenced by the quality of mixing in the bed. This largely depends on the design of gas distributor and operating conditions. Hence, in the current work, the influence of distributor design on hydrodynamics in a 3D bubbling fluidized bed column is investigated using CFD. Here, Euler-Euler model is used to predict the flow field. The predicted bed pressure drop is analyzed for various superficial gas velocities, and it has been validated with the experimental data. The solid circulation rate is calculated to quantify the flow field, and it is improved by incorporating various gas distributors such as flat, convex and concave perforated plates. The magnitude of solid circulation rate is found to be the highest for convex plate, showing that it is more advantageous than the conventional flat plate configuration. Further, the effect of operating temperature and the influence of baffle on gas–solid flow are analyzed. The rate of solid circulation is found to decrease with increase in temperature and in the presence of baffle. © 2019 Taylor & Francis Group, LLC.Item Robust optimal centralized PI controller for a fluid catalytic cracking unit(De Gruyter Open Ltd, 2021) Yadav, G.; Kiran, G.U.; Sankar Rao, C.Fluidized Catalytic Cracking (FCC) is a complex process that arises due to feed composition, non-linearities, and dynamic mass and heat interactions in its components. FCC is difficult to model and monitor in industries, and one of the key reasons is that they are multivariable processes. Such processes are highly interacting and that makes the process of controlling even more difficult. The interaction between loops can be quantified easily by dRGA. An easy and effective way of controlling multivariable processes is to implement a centralized control system, considering the interactions between measured and manipulated variables. In this study, a centralized control system is designed for the riser section of the FCC unit. The dRGA method is modified to enhance the closed-loop response by formulating an optimization problem and obtaining an optimal controller settings. A rigorous simulation studies show an 826% reduction in ISE values, a 309% reduction in IAE values, and a 262% reduction in ITAE value of T r i s ${T}_{ris}$ from the dRGA method to the modified dRGA method. Further, IAE values for Y l p g are reduced by 29% from dRGA to modified dRGA method and 34% from synthesis to modified dRGA method. © 2020 Walter de Gruyter GmbH, Berlin/Boston.Item Adsorption and desorption through packed and fluidized clay-based composite desiccant beds: a comparison study(Springer Science and Business Media Deutschland GmbH, 2022) Hiremath, C.R.; Kadoli, R.The present study considers the composite desiccant employing horse dung, sawdust with clay and later impregnating CaCl2 into the host material. The microscopic and spectroscopic experimental methods such as scanning electron microscope (SEM) and X-ray diffraction (XRD) were used to characterize the composite desiccants. The specific heat (Cp) quantification reveals higher values for clay-additives composite desiccants with lower pore volume and larger grain sizes, whereas lower values for clay composite desiccants with higher pore volume and smaller grain sizes. Adsorption–desorption experiments for moisture removal and addition are conducted in a vertical column in static and fluidized states. The desiccant beds are subjected to an initially set value of process air velocity, relative humidity, temperature and mass of bed. Moisture removal capacity, moisture addition capacity and mass transfer coefficient are the parameter indices adopted to measure the heat and mass transfer characteristics of vertical packed and fluidized bed comprising clay-additives-CaCl2 composite desiccants. Comparing packed and fluidized beds, a higher surface area of bed in fluidization improves dehumidification performance and results in higher desorption rates. Experimental results confirmed that clay and clay-additives-based desiccants have desired adsorption–desorption characteristics of a suitable desiccant. The interesting advantage of fabricated clay and clay-additives-based composite adsorbents is that the air exits the desiccant bed at a lower temperature, saving cooling energy requirements of sorption-based systems. © 2022, The Author(s), under exclusive licence to The Brazilian Society of Mechanical Sciences and Engineering.Item Transformation of refinery cracked naphtha stream into efficient lubricity improvers for ULSD(Springer, 2022) Sruthi, H.; Udayakumar, D.U.; Hegde, P.; Manjunatha, M.G.; Karthick, R.; Nandakumar, V.A new route for the conversion of refinery light cracked naphtha (LCN) stream into lubricity improvers for ultra-low sulphur diesel (ULSD) was developed through a simple chemical process involving olefin epoxidation and esterification reactions. Two different methods viz., H2O2/glacial acetic acid and m-chloroperbenzoic acid (m-CPBA), were found to be suitable for the epoxidation of LCN. The LCN epoxide was subjected to an esterification reaction via epoxide ring opening using different long chain (C4 - C18 alkyl groups) organic acids to get the hydroxy ester derivatives of LCN. The lubricating property of the newly synthesized hydroxy esters was studied by dosing them with ULSD at 300 and 150 ppm (wt/vol) concentrations. Amongst them, LCN hydroxy ester derived from stearic acid showed the best lubrication-enhancing property at both dosage levels. The scanning electron microscope (SEM) image and energy dispersive spectra (EDS) of the high-frequency reciprocating rig (HFRR) specimen support the lubricating action of the LCN esters through the formation of a protective layer between the metallic surfaces. The synergy of simple chemical processes and efficient lubricity action makes these LCN esters as promising materials for low-cost and scalable additives for ULSD. Graphical abstract: The olefin-rich light cracked naphtha obtained from the fluidized catalytic cracker unit of the oil refinery was converted into hydroxy esters through an epoxidation reaction followed by the esterification with different carboxylic acids. The hydroxy esters at low dosage levels (150/300 ppm) enhance the lubricating property of ultra-low sulfur diesel. [Figure not available: see fulltext.]. © 2022, Indian Academy of Sciences.Item A Simplified Bubble Size Relation Compatible with the Energy Minimization Multiscale Drag Model for Studying Hydrodynamics in a 2D Gas–Solid Tapered Fluidized Bed(John Wiley and Sons Inc, 2025) Sahoo, L.K.; Sarkar, S.Gas–solid fluidized bed reactors are extensively utilized in direct reduced iron production. In practice, these reactors will have a wide particle size distribution, which is better handled by tapered fluidized beds due to their vertical velocity gradient. Herein, a simplified bubble size relation is proposed to remove implicit interdependency between the bubble size and its drag coefficient in the bubble-based energy minimization multiscale (EMMS) heterogeneous drag model. Further, the proposed drag model is coupled with the two-fluid kinetic theory of granular flow model to investigate hydrodynamics. The heterogeneous flow structure predicted by the model is similar to experiments. Further, the bulk parameters such as bed expansion ratio and bubble fraction obtained from the simulations using a simplified EMMS drag model are compared and are found to be in good agreement with the experimental findings, with mean relative deviations of 3.95% and 14.64%, respectively. The time-averaged bubble fraction and bed expansion ratio are found to increase with air velocity and decrease with taper angle, whereas a reverse trend is observed for the mean particulate fluidized area fraction. Based on the current study, the taper angle between 5° and 10° is found to be most suitable. © 2024 Wiley-VCH GmbH.